Choosing a Calibration
All Vo's in the two-month period that pass the statistical elimination are corrected to an circular orbit (because of the yearly variation in the earth-sun distance) and then averaged to a "representative" orbit-normalized calibration Vo for that period.
"Representative" Vo's for each channel (square symbols) are then plotted in time series over two year periods, as shown in the example below.
The sinusoidal lines are best fit functions used to interpolate spectral Vo's to specific days. Interpolated daily Vo values are corrected back to the earth-sun distance appropriate to the day being processed, and then combined with MFRSR measurements to produce daily time series of total optical depth, from which AOD is derived.